<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .content {
      display: flex;
      width: 100%;
      height: 800px;
      background-color: skyblue;
    }

    .left,
    .right {
      width: 200px;
      height: 100%;
      background-color: pink;
    }

    .middle {
      flex: 1;
      background-color: yellow;
    }
  </style>
</head>

<body>
  <div class="content">
    <div class="left">左边</div>
    <div class="middle">中间我是谁我也不知道我就想试试看这个到底是什么样子的哈哈哈你知道吗css是的咸阳市我也不知道是啥怎么实现三列布局</div>
    <div class="right">右边</div>
  </div>
</body>

</html>